“Impossible objects” like the etchings of M.C. Escher have fascinated adults for centuries. You can’t help but stare and wonder at a drawing like this, which seems to defy the laws of nature:

The drawing seems strange to us because our visual system tells us that when an object or part of an object occludes another, it’s in front. Since the parts of the cube are all connected, it’s clear that the vertical bar in the “back” of the cube shouldn’t be in front of any other bars.

Some research has suggested that young babies don’t have the same ability as adults to determine how close objects are to them. Babies younger than 6 months, for example, aren’t able to reach the right distance for objects after seeing a three-dimensional display. But babies do recognize real objects after seeing pictures, and they recognize possible and impossible events involving solid objects. Can they recognize impossible objects?

A team led by Sarah Shuwairi showed an image like the one above to 10 four-month-olds, but with one crucial difference: the portion of the image determining whether the object was possible or impossible was obscured with a red oval:

This image was shown to them repeatedly, at least five times, until they were obviously quite bored with it (they were “habituated”). Then they were shown the entire, unobscured object. The “possible” cube was alternated with the “impossible” cube six times, so each cube was viewed a total of three times. An experimenter watching on video pressed a button when the baby looked at the cubes, so that the total looking time for each type of object could be computed. Here are the results:

The babies looked significantly longer at the impossible cube, suggesting that this was a surprising or novel object to them.

The study was repeated on a new set of infants, but instead of using a realistic image, they were just shown a line-drawing. This offers much less detail, and only one method of determining whether the object is possible or impossible. This time some infants were habituated as before, while others were just shown the possible and impossible objects without habituation. Here are those results:

In both cases, once again, the babies looked at the impossible objects longer than the than the possible objects — suggesting that these objects were novel or surprising to them.

The researchers say this demonstrates that infants are able to use the relative placement of objects (occlusion) to make judgments about how far away the objects are. Even at this early age, their visual system is able to make some of the same types of depth judgments as adults are.

Perhaps more importantly, this suggests that very young infants might already be able to appreciate the work of M.C. Escher!

Comments

I fail to see how the authors conclude from the results that infants necessarily use occlusion to make judgments about distance. Since infants develop object permanence as early as 3 months, wouldn’t that suggest that infants “know” that occluded objects still obey some principles. In that case, maybe the novelty results from a simple computation on the occlusion boundaries. Certainly that would fall in line with the idea that language acquisition results from innate learning about word statistics. Why wouldn’t the infants apply that type of statistical learning to other domains? (faces are another example where statistical learning might explain novelty effects, but for inversion instead of impossible occlusions.)

I fail to see how the authors conclude from the results that infants necessarily use occlusion to make judgments about distance.

Yeah. This is puzzling at first glance.

The information in the textbook I teach from indicates that pictoral depth sensitivity emerges at 6-7 months. So the fact that 4 month olds in this study are showing sophisticated pictoral depth perception surprises me. Furthermore, the author indicates that the development of pictoral depth cues probably depends on motor development (e.g., crawling, grasping objects) that allows infants to experience their surroundings. If we are to go with the textbook info, it would make more sense to say that understanding distance via environmental exploration leads to an understanding of occlusion (in two dimensions). The authors’ conclusion seems to be suggesting the diametrically opposite conclusion that understanding occlusion (in two dimensions) leads to an understanding of distance.

To make sense of this contradiction, my best guess is that children are probably learn more about the nature of particular objects (around 3 months when they have the ability to grasp and look at objects), before they learn about depth perception (which requires crawling about the environment around 6 months). So probably it’s the grasping and looking at objects around 3 months that is the basis for the present results and not depth-perception, per se. Might be interesting to see how they respond to illusions associated with size and shape constancy which are more associated with depth perception.

I’d be very interested in seeing what the results would look like if the stimuli were the impossible cube vs. the Necker Cube. At first glance, both cubes look almost identical (except the Necker cube creates the illusion of a cube moving toward and away from you).

(Actually I just noticed something quite odd when I was looking at the pictures of the Necker Cube and impossible cube presented on wikipedia. For me, the impossible cube seems to look possible when you switch your attention between both for awhile).

My view is based on generalisations about development of intellect. Neural networks develop their strength based on input; valid and verifyable inputs strengthen, invalid ones do not contribute.
The visual system as well as all sensory systems begin to process cues at the moment of completion of hardwired components, which for many of these systems is prior to birth. This is evidenced by the many anecdotal and scientifically researched reports on the auditory system’s capabilities. Visual system development takes off full bore after birth and becomes more and more reliable as visual acuity improves but is not incapable of discerning reality from irreality.
As the Escher figure represents irrealty, the cues generated are sufficient for the visual system to decide the validityof the input. An interesting line of research would be to vary the degree of “weirdness”, the degree varying from subtle to overt and observe the evaluation of the inputs by the test subjects.